Loudspeakers are susceptible to a variety of forms of distortion, which can be irritating to a listener. For example, distortion in loudspeakers in cell phones can lead not only to poor quality reproduction, but can be so bad that the speech is unintelligible. With the movement towards smaller and cheaper loudspeakers in today's consumer electronics, the problem is exacerbated.
At present, loudspeakers are measured for distortion in the factory, if at all, and those that don't meet specifications are simply discarded. In other audio disciplines, small microphones are used to measure noise in noise canceling applications.